appliance, rotor and magnet element

ABSTRACT

A magnet element ( 37 ) and a method of its manufacture for assembly into a rotor ( 38 ), the magnet element ( 37 ) having magnetic domains aligned anisotropically to form a domain alignment pattern ( 42 ), wherein the magnetic domain alignment pattern ( 42 ) in the magnet element ( 37 ) has an orientation that varies substantially continuously across at least part of the magnet element ( 37 ) between its lateral edges from at least partially radial to at least partially tangential.

FIELD OF THE INVENTION

The present invention relates to electric motors and magnet elements foruse in such motors, and particularly motors having an external rotor ofa type that are used as the main drive motor for a domestic laundrymachine or other apparatus.

BACKGROUND TO THE INVENTION

EP 1548171 describes a drive system for washing machines. The drivesystem comprises a motor with a large diameter shallow stator and arotor with magnets external to the stator. The stator is supported onthe end of a washing tub as shown in FIG. 2 of that application. Thestator has an aperture for a drive shaft to pass through. As shown inFIGS. 2 and 16 of EP patent application 1548171, a rotor, which is to befixed to the rotating drum of a washing machine, has a ring of permanentmagnet material supported on the inside of a steel backing ring. A frameextends between the hub of the rotor (through which the shaft canextend) and the steel backing ring. The backing ring and frame may beformed together. The permanent magnet material is made of a set ofcurved permanent magnet elements. The permanent magnet material ismagnetised after physical construction of the rotor. A typical rotor hasmore than 30 poles magnetised into the ring of magnetic material. Thepolarity of the poles alternates proceeding around the ring.

The magnet elements are typically made of hard ferrite permanent magnetmaterial. The magnets may be isotropic or anisotropic. In anisotropic,the magnet elements are formed with their magnetic domains alignedacross the thickness of the magnet so as to be aligned radiallygenerally as shown by arrow “A” in FIG. 1 of the present application.Magnetisation of the rotor follows this pattern to create radialmagnetic field lines through the thickness of the magnet, represented bythe magnetic flux lines or paths in FIG. 1. This results in a pattern ofpoles on the outside face of the magnets (adjacent the backing steel)that is the inverse of the pattern of poles on the inside of the face ofthe magnets (facing radial inwards).

In the case of radial magnetisation, the portion of each magnet close tothe interface between magnets is known to provide little benefit interms of the flux coupled from the rotor into the stator and cantypically be removed with little loss in torque production.

Halbach arrays have been created to at least partially alleviate thisproblem. One example of a Halbach array is an arrangement of magnetswith their respective directions of magnetisation oriented as shown inFIG. 2 a of the present application. As shown in FIG. 2 b of the presentapplication, a total resulting magnetic flux field is produced thatreduces the magnetic flux that couples out the back face of the magneticring. Isotropic or anisotropic magnetic sections can be used in such anarray. Anisotropic sections have magnetic domains aligned in onedirection, whereas isotropic sections have magnetic domains arrangedrandomly. FIG. 2 c shows a portion of an “ideal” Halbach array resultingmagnetic flux field where a large or infinite number of magneticelements are formed into a Halbach array.

It has been proposed that a single piece isotropic ring can bemagnetised to produce a Halbach array “style” magnetic field. Thesections of single piece ring are magnetised using an external magneticfield. Performance of the isotropic ring will be limited relative toradially magnetised anisotropic magnets due to the reduced magneticstrength of the isotropic magnets.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a magnet element, ora rotor or a motor with such an element, or an appliance that uses sucha motor or rotor, where the magnet element has pre-aligned domains toenable production of an improved resulting magnetic flux field in arotor or part of a rotor, or to at least provide the industry with auseful choice.

In one aspect the present invention may be said to consist in a rotorcomprising: a plurality of magnet elements with two lateral edges eachwith magnetic domains aligned anisotropically to form a domain alignmentpattern, the plurality of magnets being arranged to form a permanentmagnet ring with an inner face and an outer face, said permanent magnetring being between 150 mm and 400 mm in diameter, less than 100 mm inheight and less than 20 mm thick, and a rigid support holding saidmagnet elements in said ring arrangement, wherein the magnetic domainalignment pattern in each magnet element has an orientation that variessubstantially continuously across at least part of the magnet elementbetween its lateral edges from an orientation that has a predominantradial component at a pole of the magnet element to an orientation thathas a least some tangential component at one lateral edge of the magnetelement, wherein the magnet elements are magnetised to produce aresulting magnetic flux field.

Preferably, the magnet elements have a chamfer at the intersection ofeach lateral edge with the front edge, wherein the front edge is theedge at the inner face of the rotor.

Preferably, each magnet element has the pole positioned between themagnet element's lateral edges and the magnetic domain alignment patternin each magnet element has an orientation that varies substantiallycontinuously across the width of the magnet element from an orientationthat has a predominant radial component at the pole of the magnetelement to an orientation that has a least some tangential component atboth lateral edges of the magnet element.

Preferably, at both lateral edges, the orientation of the magneticdomain alignment pattern has a significant tangential component.

Preferably, at both lateral edges the significant tangential componentresults in the magnetic domain alignment pattern having an orientationof at least 15 degrees with respect to the lateral edges.

Preferably, both lateral edges the significant tangential componentresult in the magnetic domain alignment pattern having an orientation ofbetween 20 to 35 degrees, and more preferably substantially 30 degrees,with respect to the lateral edges.

Preferably, at both lateral edges, the orientation of the magneticdomain alignment pattern has a predominant tangential component.

Preferably, each magnet element has the pole positioned at or towardsone lateral edge.

Preferably, the orientation of the magnetic domain alignment pattern hasa significant tangential component at the lateral edge.

Preferably, the orientation varies substantially non-linearly over themagnet element.

Preferably, the radial and tangential components of the orientation ofthe magnetic domain alignment pattern within the magnet element variessinusoidally according to:

V _(R)=cos(θ), and

V _(T)=sin(θ)

Where V_(R) and V_(T) are the radial and tangential components of theorientation respectively and θ is the angular position across the magnetelement, varying from substantially −90 degrees at one lateral edge tosubstantially +90 degrees at the opposite lateral edge.

Preferably, one or more spacer elements are arranged between the lateraledges of one or more proximate magnetic elements arranged to form thepermanent magnet ring.

Preferably, the spacer elements are magnetic with a magnetic domainalignment pattern with a substantially tangential orientation across thespacer element.

Preferably, the resulting magnetic flux field is created by applying anexternal magnetic flux field that has a geometry within each magnetelement that is substantially similar to the magnetic domain alignmentpattern within that element.

Preferably, the resulting magnetic flux field is a Halbach-style fluxfield.

Preferably, the resulting magnetic flux field has poles with alternatingpolarity spaced around the ring, the poles being aligned radially withrespect to the permanent magnet ring, and wherein the resulting magneticflux field of the permanent magnet ring traverses between adjacent polesof opposite polarities and between those poles is focused to extendbeyond the boundary defined by the inner face, but remain at leastpartially constrained within the boundary defined by the outer face ofthe permanent magnet ring,

Preferably, the magnetic domain alignment pattern assists creation of astronger resulting magnetic flux field when the magnet elements aremagnetised.

Preferably, the portion of the resulting magnetic flux field in eachmagnet element has an orientation that varies substantially continuouslyover the magnet element wherein: across the width of the magnet element,the orientation varies from an orientation that has a predominant radialcomponent at the pole to an orientation that has a predominanttangential component at the edges of the magnet element adjacent othermagnet elements in the permanent magnet ring, and across the depth ofthe magnet element, the orientation varies from an orientation that hasa predominant radial component at an edge corresponding to the innerface of the permanent magnet ring to an orientation that has apredominant tangential component at an edge corresponding to the outerface of the permanent magnet ring.

Preferably, the orientation varies substantially non-linearly over themagnet element.

Preferably, the portion of the resulting magnetic flux field betweenadjacent poles extending beyond the boundary defined by the inner faceof the permanent magnet ring magnet element has an orientation thatvaries continuously wherein: between the poles, the orientation variesfrom an orientation that has a predominant radial component at the poleto an orientation that has a predominant tangential component at themid-point between the poles, and extending radially from the inner face,the orientation varies from an orientation that has a predominant radialcomponent at an inner face to an orientation that has an increasinglytangential component with distance from the inner face.

Preferably, the orientation varies substantially non-linearly betweenthe poles and extending beyond the inner face.

Preferably, the radial and tangential components of the orientation ofthe resulting magnetic flux field at or proximate the inner surface ofthe magnet element varies sinusoidally according to:

V _(R)=cos(θ), and

V _(T)=−sin(θ)

Where V_(R) and V_(T) are the radial and tangential components of theorientation respectively and θ is the angular position across the magnetelement, varying from substantially −90 degrees at one lateral edge tosubstantially +90 degrees at the opposite lateral edge.

Preferably, for each magnet element, the magnetic domains were alignedduring production of the magnet element.

Preferably, for each magnet element, the magnetic domains were alignedduring production using a press or injection moulding tool comprisingone or more elements defining a cavity; and an apparatus for applying amagnetic flux field, wherein the apparatus produces a magnetic field inthe cavity similar in nature to the desired magnetic domain alignmentpattern in the element.

Preferably, the rotor is utilised in the drive motor of a washingmachine comprising an electronically commutated motor, a stator of themotor having windings energisable to cause rotation of the rotor, saidstator being coupled to a non-rotating tub or housing of the washingmachine, said rotor being coupled to a rotating drum of the washingmachine.

Preferably, the washing machine is a top loading washing machinecomprising: an outer wrapper, a tub suspended in the outer wrapper, anda rotating drum in the tub.

Preferably, the washing machine is a horizontal axis machine comprising:an outer wrapper, a rotating drum housing, and a rotating drum in thehousing.

Preferably, the washing machine is a horizontal axis machine with toploading access comprising: an outer wrapper, a tub, and a rotating drumin the tub.

Preferably, utilised in a power generation apparatus.

In another aspect the present invention may be said to consist in amotor for use in a washing machine, said motor comprising: a statorhaving at least three phase windings, each phase winding being formed ona plurality of radially extending stator teeth, a rotor as defined inany preceding claim, concentric with said stator with the permanentmagnet ring outside said stator teeth and said rotor poles facing theends of said stator teeth.

In another aspect the present invention may be said to consist in amethod of producing a rotor comprising the steps of: producing aplurality of magnet elements comprising permanent magnet material withtwo lateral edges each with magnetic domains aligned anisotropically toform a domain alignment pattern, wherein the magnetic domain alignmentpattern in each magnet element has an orientation that variessubstantially continuously across at least part of the magnet elementbetween its lateral edges from an orientation that has a predominantradial component at a pole of the magnet element to an orientation thathas a least some tangential component at one lateral edge of the magnetelement, arranging and retaining the magnet elements into a permanentmagnet ring in a rigid support, and magnetising the magnet elements toproduce a resulting magnetic flux field.

Preferably, the magnet elements have a chamfer at the intersection ofeach lateral edge with the front edge, wherein the front edge is theedge at the inner face of the rotor.

Preferably, the step of producing the plurality of magnet elementcomprises applying an external magnetic flux field to each magnetelement to align the magnetic domains.

Preferably, each magnet element has the pole positioned between themagnet element's lateral edges and applying the external magnetic fluxfield to a magnet elements aligns its magnetic domains such that themagnetic domain alignment pattern in the magnet element has anorientation that varies substantially continuously across the width ofthe magnet element from an orientation that has a predominant radialcomponent at the pole of the magnet element to an orientation that has aleast some tangential component at both lateral edges of the magnetelement.

Preferably, at both lateral edges, the orientation of the magneticdomain alignment pattern has a significant tangential component.

Preferably, at both lateral edges the significant tangential componentresults in the magnetic domain alignment pattern having an orientationof at least 15 degrees with respect to the lateral edges.

37. A method according to claim 34 or 35 wherein at both lateral edgesthe significant tangential component result in the magnetic domainalignment pattern having an orientation of between 20 to 35 degrees, andmore preferably substantially 30 degrees, with respect to the lateraledges.

Preferably, at both lateral edges, the orientation of the magneticdomain alignment pattern has a predominant tangential component.

Preferably, each magnet element has the pole positioned at or towardsone lateral edge.

Preferably, the orientation varies substantially non-linearly over themagnet element.

Preferably, the radial and tangential components of the orientation ofthe magnetic domain alignment pattern within the magnet element variessinusoidally according to:

V _(R)=cos(θ), and

V _(T)=sin(θ)

Where V_(R) and V_(T) are the radial and tangential components of theorientation respectively and θ is the angular position across the magnetelement, varying from substantially −90 degrees at one lateral edge tosubstantially +90 degrees at the opposite lateral edge.

Preferably, the resulting magnetic flux field is created by applying anexternal magnetic flux field that has a geometry within each magnetelement that is substantially similar to the magnetic domain alignmentpattern within that element.

Preferably, the resulting magnetic flux field is a Halbach-style fluxfield.

Preferably, the resulting magnetic flux field has poles with alternatingpolarity spaced around the ring, the poles being aligned radially withrespect to the permanent magnet ring, and wherein the resulting magneticflux field of the permanent magnet ring traverses between adjacent polesof opposite polarities and between those poles is focused to extendbeyond the boundary defined by the inner face, but remain at leastpartially constrained within the boundary defined by the outer face ofthe permanent magnet ring,

Preferably, the magnetic domain alignment pattern assists creation of astronger resulting magnetic flux field when the magnet elements aremagnetised.

Preferably, the portion of the resulting magnetic flux field in eachmagnet element has an orientation that varies substantially continuouslyover the magnet element wherein: across the width of the magnet element,the orientation varies from an orientation that has a predominant radialcomponent at the pole to an orientation that has a predominanttangential component at the edges of the magnet element adjacent othermagnet elements in the permanent magnet ring, and across the depth ofthe magnet element, the orientation varies from an orientation that hasa predominant radial component at an edge corresponding to the innerface of the permanent magnet ring to an orientation that has apredominant tangential component at an edge corresponding to the outerface of the permanent magnet ring.

Preferably, the orientation varies substantially non-linearly over themagnet element.

Preferably, the portion of the resulting magnetic flux field betweenadjacent poles extending beyond the boundary defined by the inner faceof the permanent magnet ring magnet element has an orientation thatvaries continuously wherein: between the poles, the orientation variesfrom an orientation that has a predominant radial component at the poleto an orientation that has a predominant tangential component at themid-point between the poles, and extending radially from the inner face,the orientation varies from an orientation that has a predominant radialcomponent at an inner face to an orientation that has an increasinglytangential component with distance from the inner face.

Preferably, the orientation varies substantially non-linearly betweenthe poles and extending beyond the inner face.

Preferably, the radial and tangential components of the orientation ofthe resulting magnetic flux field at or proximate the inner surface ofthe magnet element varies sinusoidally according to:

V _(R)=cos(θ), and

V _(T)=−sin(θ)

Where V_(R) and V_(T) are the radial and tangential components of theorientation respectively and θ is the angular position across the magnetelement, varying from substantially −90 degrees at one lateral edge tosubstantially +90 degrees at the opposite lateral edge.

In another aspect the present invention may be said to consist in arotor comprising: a plurality of magnet elements with two lateral edgeseach with magnetic domains aligned anisotropically to form a domainalignment pattern, the plurality of magnets being arranged to form apermanent magnet ring with an inner face and an outer face, and a rigidsupport holding said magnet elements in said ring arrangement, whereinthe magnetic domain alignment pattern in each magnet element has anorientation that varies substantially continuously across at least partof the magnet element between its lateral edges from an orientation thathas a predominant radial component at a pole of the magnet element to anorientation that has a least some tangential component at one lateraledge of the magnet element, wherein the magnet elements are magnetisedto produce a resulting magnetic flux field.

In another aspect the present invention may be said to consist in amagnet element for assembly into a ring of magnet elements to form partof a rotor, the magnet element having two lateral edges each withmagnetic domains aligned anisotropically to form a domain alignmentpattern, wherein the magnetic domain alignment pattern in the magnetelement has an orientation that varies substantially continuously acrossat least part of the magnet element between its lateral edges from anorientation that has a predominant radial component at a pole of themagnet element to an orientation that has a least some tangentialcomponent at one lateral edge of the magnet element.

Preferably the element has a chamfer at the intersection of each lateraledge with a front edge, wherein the front edge is the edge at the innerface of the rotor.

Preferably, the pole is positioned between the magnet element's lateraledges and the magnetic domain alignment pattern in each magnet elementhas an orientation that varies substantially continuously across thewidth of the magnet element from an orientation that has a predominantradial component at the pole of the magnet element to an orientationthat has a least some tangential component at both lateral edges of themagnet element.

Preferably, at both lateral edges, the orientation of the magneticdomain alignment pattern has a significant tangential component.

Preferably, at both lateral edges the significant tangential componentresults in the magnetic domain alignment pattern having an orientationof at least 15 degrees with respect to the lateral edges.

Preferably, at both lateral edges the significant tangential componentresult in the magnetic domain alignment pattern having an orientation ofbetween 20 to 35 degrees, and more preferably substantially 30 degrees,with respect to the lateral edges.

Preferably, at both lateral edges, the orientation of the magneticdomain alignment pattern has a predominant tangential component.

Preferably, each magnet element has a pole positioned at or towards onelateral edge.

Preferably, the orientation of the magnetic domain alignment pattern hasa significant tangential component at the lateral edge.

Preferably, the orientation varies substantially non-linearly over themagnet element.

Preferably, the radial and tangential components of the orientation ofthe magnetic domain alignment pattern within the magnet element variessinusoidally according to:

V _(R)=cos(θ), and

V _(T)=sin(θ)

Where V_(R) and V_(T) are the radial and tangential components of theorientation respectively and θ is the angular position across the magnetelement, varying from substantially −90 degrees at one lateral edge tosubstantially +90 degrees at the opposite lateral edge.

Preferably, the resulting magnetic flux field is created by applying anexternal magnetic flux field that has a geometry within each magnetelement that is substantially similar to the magnetic domain alignmentpattern within that element.

Preferably, the resulting magnetic flux field is a Halbach-style fluxfield.

Preferably, the resulting magnetic flux field has poles with alternatingpolarity spaced around the ring, the poles being aligned radially withrespect to the permanent magnet ring, and wherein the resulting magneticflux field of the permanent magnet ring traverses between adjacent polesof opposite polarities and between those poles is focused to extendbeyond the boundary defined by the inner face, but remain at leastpartially constrained within the boundary defined by the outer face ofthe permanent magnet ring,

Preferably, the magnetic domain alignment pattern assists creation of astronger resulting magnetic flux field when the magnet elements aremagnetised.

Preferably, the portion of the resulting magnetic flux field in eachmagnet element has an orientation that varies substantially continuouslyover the magnet element wherein: across the width of the magnet element,the orientation varies from an orientation that has a predominant radialcomponent at the pole to an orientation that has a predominanttangential component at the edges of the magnet element adjacent othermagnet elements in the permanent magnet ring, and across the depth ofthe magnet element, the orientation varies from an orientation that hasa predominant radial component at an edge corresponding to the innerface of the permanent magnet ring to an orientation that has apredominant tangential component at an edge corresponding to the outerface of the permanent magnet ring.

Preferably, the orientation varies substantially non-linearly over themagnet element.

Preferably, the portion of the resulting magnetic flux field betweenadjacent poles extending beyond the boundary defined by the inner faceof the permanent magnet ring magnet element has an orientation thatvaries continuously wherein: between the poles, the orientation variesfrom an orientation that has a predominant radial component at the poleto an orientation that has a predominant tangential component at themid-point between the poles, and extending radially from the inner face,the orientation varies from an orientation that has a predominant radialcomponent at an inner face to an orientation that has an increasinglytangential component with distance from the inner face.

Preferably, the orientation varies substantially non-linearly betweenthe poles and extending beyond the inner face.

Preferably, the radial and tangential components of the orientation ofthe resulting magnetic flux field at or proximate the inner surface ofthe magnet element varies sinusoidally according to:

V _(R)=cos(θ), and

V _(T)=−sin(θ)

Where V_(R) and V_(T) are the radial and tangential components of theorientation respectively and θ is the angular position across the magnetelement, varying from substantially −90 degrees at one lateral edge tosubstantially +90 degrees at the opposite lateral edge.

In another aspect the present invention may be said to consist in amethod of producing a magnet element comprising aligning the magneticdomains of the element in the manner defined above.

Preferably, comprising producing a magnet element in a press orinjection moulder from magnetic material, and applying a magnetic fluxfield approximately in the direction of the desired magnetic domainalignment pattern.

In another aspect the present invention may be said to consist in arotor comprising: a plurality of magnet elements with two lateral edgeseach with magnetic domains aligned anisotropically to form a domainalignment pattern, the plurality of magnets being arranged to form apermanent magnet arrangement, and a rigid support holding said magnetelements in said arrangement, wherein the magnetic domain alignmentpattern in each magnet element has an orientation that variessubstantially continuously across at least part of the magnet elementbetween its lateral edges from an orientation that has at least sometangential component at a point in the magnet element to an orientationthat has a predominant radial component at poles positioned at thelateral edges of the magnet element, wherein the magnet elements aremagnetised to produce a resulting magnetic flux field.

In another aspect the present invention may be said to consist in amagnet element for assembly into a ring of magnet elements to form partof a rotor, the magnet element having two lateral edges each withmagnetic domains aligned anisotropically to form a domain alignmentpattern, wherein the magnetic domain alignment pattern in the magnetelement has an orientation that varies substantially continuously acrossat least part of the magnet element between its lateral edges from anorientation that has at least some tangential component at a point inthe magnet element to an orientation that has a predominant tangentialcomponent at poles positioned at the lateral edges of the magnetelement.

In another aspect the present invention may be said to consist in arotor comprising: a plurality of magnet elements with two lateral edgeseach with magnetic domains aligned anisotropically to form a domainalignment pattern, the plurality of magnets being arranged to form apermanent magnet ring with an inner face and an outer face, and a rigidsupport holding said magnet elements in said ring arrangement, whereinthe magnetic domain alignment pattern in each magnet element has anorientation that varies substantially continuously across at least partof the magnet element between its lateral edges from an orientation thathas a predominant radial component at a pole of the magnet elementpositioned between the lateral edges to an orientation that has a leastsome tangential component at the lateral edges of the magnet element,wherein the magnet elements are magnetised to produce a resultingmagnetic flux field.

Preferably, the magnetic domains are substantially aligned as shown inone of FIGS. 4 a to 4 f or 15 a to 15 d.

Preferably, the magnetic domain alignment pattern deviates from theHalbach-style resulting magnetic flux field.

Preferably the magnetic domain alignment pattern deviates from theHalbach-style resulting magnetic flux field.

Preferably, the magnetic domain alignment pattern deviates from theHalbach-style resulting magnetic flux field.

Preferably, for each magnet element, the magnetic domains were alignedduring production of the magnet element.

Preferably, for each magnet element, the magnetic domains were alignedduring production using a press or injection moulding tool comprisingone or more elements defining a cavity, and an apparatus for applying amagnetic flux field, wherein the apparatus produces a magnetic field inthe cavity similar in nature to the desired magnetic domain alignmentpattern in the element.

An anisotropic magnet element in accordance with the present inventioncan, when arranged in a rotor, result in or allow production of aHalbach-style resulting magnetic flux field that is much stronger thansuch a flux field produced in an isotropic or radially alignedanisotropic magnet. Therefore, in aligning the magnetic domains asdescribed to create an anisotropic Halbach magnetised rotor, theresulting flux field is much stronger than that achievable by thepreviously alternatively proposed isotropic magnet ring or an equivalentradially magnetised anisotropic ring.

This provides a higher performance rotor/motor. Low togging is alsoobtainable.

In this specification where reference has been made to patentspecifications, other external documents, or other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the invention. Unless specifically statedotherwise, reference to such external documents is not to be construedas an admission that such documents, or such sources of information, inany jurisdiction, are prior art, or form part of the common generalknowledge in the art.

The term “comprising” as used in this specification means “consisting atleast in part of”. Related terms such as “comprise” and “comprised” areto be interpreted in the same manner.

It is intended that reference to a range of numbers disclosed herein(for example, 1 to 10) also incorporates reference to all rationalnumbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5,7, 8, 9 and 10) and also any range of rational numbers within that range(for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescriptions herein are purely illustrative and are not intended to bein any sense limiting

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical magnet element for a rotor,

FIG. 2 a shows a Halbach array with a finite number of elements,

FIG. 2 b shows the resulting magnetic flux field of the Halbach array inFIG. 2 a,

FIG. 2 c shows a portion of a resulting magnetic flux field of an idealHalbach array with a large or infinite number of elements,

FIGS. 3 a-3 c show a rotor and stator, where the rotor incorporates amagnet element according to an embodiment of the invention,

FIGS. 3 d and 3 e show another rotor and stator, where the rotorincorporates a magnet element according to an embodiment of theinvention,

FIG. 3 f shows another rotor that incorporates a magnet elementaccording to an embodiment of the invention,

FIG. 4 a shows a magnetic domain alignment pattern formed in a magnetelement according to an embodiment of the invention,

FIG. 4 b shows a magnetic domain alignment pattern formed in a pair ofmagnet elements according to one embodiment,

FIGS. 4 c-4 f show magnetic domain alignment patterns according toalternative embodiments,

FIG. 5 a shows a portion of a rotor comprising a number of magnetelements as shown in FIG. 4 a, and the resulting magnetic flux field,

FIG. 5 b shows a predicted resulting magnetic flux field of the portionof the rotor with a stator present,

FIG. 6 a shows a resulting magnetic flux field existing in a magnetelement of a ring when magnetised,

FIG. 6 b shows the magnet element of FIG. 6 a with its magnetic domainalignment pattern superimposed on the resulting magnetic flux field,

FIG. 6 c shows a graph indicating the relationship between the fluxlinkage and orientation of the magnetic flux field at the edge of amagnet element,

FIGS. 6 d, 6 e show graphs of the tangential and radial components ofthe resulting magnetic flux field along the inner surface of a magnetelement, along with a comparison of tangential and radial components ofthe resulting magnetic flux field in standard elements with radiallyaligned magnetic domains,

FIG. 7 a shows a first apparatus for producing a magnet element with amagnetic domain alignment pattern the same as or similar to one of thoseshown in FIG. 4 a-4 e,

FIGS. 7 b and 7 c show the magnetic domain alignment pattern duringproduction of a magnet element using the apparatus in FIG. 7 a,

FIG. 8 a shows a second apparatus for producing a magnet element with amagnetic domain alignment pattern the same as or similar to one of thoseshown in FIG. 4 a-4 e,

FIGS. 8 b and 8 c show the magnetic domain alignment pattern duringproduction of a magnet element using the apparatus in FIG. 8 a,

FIG. 9 shows a diagrammatic cutaway view of a washing machine of avertical axis type that may incorporate a rotor and/or motor accordingto the present invention,

FIG. 10 shows a diagrammatic view of a horizontal axis washing machinewith front access that may incorporate the rotor and/or motor accordingto the present invention,

FIG. 11 shows a diagrammatic view of a horizontal axis washing machinewith top or tilt access that may incorporate the rotor and/or motoraccording to the present invention,

FIG. 12 shows a diagrammatic view of a horizontal axis laundry machinewith tilt access that may incorporate the rotor and/or motor accordingto the present invention,

FIG. 13 shows a graph of the relative cogging performances of Halbachand standard magnetic field patterns,

FIG. 14 shows two graphs indicating the desired B—H characteristics of amagnetic material used for a magnet element,

FIGS. 15 a-15 d show alternative magnet elements with magnetic domainalignment patterns,

FIG. 16 shows a diagrammatic view of a magnetiser for magnetising therotor,

FIG. 17 shows a magnet element with a chamfer according to anotherembodiment,

FIGS. 18 a to 18 c show resulting magnetic flux fields for adjacentmagnet elements with chamfers and magnetic domain edge angles of 30, 60and 90 degrees respectively,

FIG. 19 shows a graph of the cogging torque for chamfered andnon-chamfered magnet elements,

FIG. 20 shows a perspective view of a chamfered magnet element,

FIG. 21 shows chamfered magnet elements keyed onto a core ring,

FIG. 22 shows a demagnetisation curve for three different magnetmaterials,

FIG. 23 shows the flux linkage versus angle and magnet grade required toavoid demagnetisation,

FIG. 24 shows an alternative arrangement for the backing steel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment of the invention, a motor is provided such as thatshown diagrammatically in FIGS. 3 a to 3 c. FIGS. 3 a, 3 b show the topand bottom of the rotor 36, while FIG. 3 c shows the stator 31. Themotor could be used in a washing machine, for example. The stator 31comprises a number of poles e.g. 32, each pole comprising a coil orwinding 33 wound around a radially extending core or tooth 34. Thewindings are typically arranged to form multiple sets of windings, orphases. Three phases are commonly used. Each tooth extends from anannular ring 35 or other suitable support frame. Each winding may beindependently energised. The stator core can be formed from any suitablematerial.

The rotor 36 comprises a number of, hard ferrite or neodymium-iron-boronpermanent magnet elements, e.g. 37, arranged to form a permanent magnetring 38 of such elements. The permanent magnet elements 37 could also becomprised of a blend of hard ferrite and neodymium-iron-boron materialor other magnetic material such as, but not limited to, Samarium-cobalt.Alternatively the permanent magnet elements 37 could comprise a blend ofthese magnet materials and plastic material. The ring 38 of magneticmaterial can be supported by a rigid rotor support or housing 39. Thismay comprise an over moulded plastics annular ring, with a plastics hub.Alternatively, the housing could comprise pressed steel 39 a (as in therotor of FIG. 3 e) with the magnet elements attached therein. A singleor multiple piece or multiple layer laminated backing ring 40 (see FIG.3 a) could optionally be provided to increase the resulting magneticflux field produced by the magnetic material. Preferably, the ring ofpermanent magnetic material 38 has a diameter of between 150 mm and 400mm, a height being less than 100 mm. Each said section (and said ring)is preferably less than 20 mm thick. It will be appreciated by thoseskilled in the art that there are many possible variations on theconstruction of a stator 31 and rotor 36 for use in a washing machinemotor.

FIGS. 3 a-3 c show just one possibility in a general form for exemplarypurposes. FIGS. 3 d-3 e show an alternative possible rotor. It should benoted that FIG. 3 a-3 c shows a magnet to stator ratio of 4:3. Otherratios are possible also, for example 6:7, 9:10 or any other suitableratio. It should also be noted that the number of stators and magnetsshown in FIGS. 3 d and 3 e are illustrative only to demonstrate thephysical nature of the rotor/stator. The actual number of stator polesand magnets might be different. The rotor 36 can be magnetised toproduce a Halbach-style resulting magnetic flux field the same orsimilar to that produced by a standard Halbach array.

Each permanent magnet element 37 in the rotor is produced in a mannersuch that it comprises magnetic domains, e.g. 41, pre-aligned into amagnetic domain alignment pattern 42 as shown generally in FIG. 4 a. Theterm “magnetic domain alignment pattern” refers to the orientation ofthe magnetic domains 41 occurring as a result of the manufactureprocess. Multiple magnet elements 37 can be arranged together, such asshown in FIG. 4 b, where two permanent magnet elements 37 with magneticdomains 41 pre-aligned into the domain alignment pattern 42 shown havebeen arranged side-by-side. This creates magnetic material withpre-aligned magnetic domains 41 that enable production of aHalbach-style resulting magnetic flux field when the magnet material issubsequently magnetised by a magnetisation pattern. A ring of suchmagnet elements 37 can be assembled to produce a permanent magnet ring38 of the rotor 36. This can be magnetised to have a Halbach-styleresulting magnetic flux field. This field is stronger than if isotropicor radially aligned anisotropic magnetic material is magnetised with thesame flux field. A rotor 36 with Halbach-style resulting magnetic fluxfield is the desired field in order to produce improved operatingcharacteristics of the motor. The magnet elements 37 of the permanentmagnet ring 38 might be curved commensurate with the curvature of therotor 36.

“Halbach style” refers to a resulting magnetic flux field that is thesame as or is similar to a magnetic flux field produced by a traditionalHalbach array magnet arrangement. The term “magnetisation pattern”refers to the external magnetic flux field employed to energise themagnet element according to the domain alignment pattern, causing themagnets to become magnetised. The term “resulting magnetic flux field”refers to the magnetic flux field that exists in the magnet elements 37(and surrounding structure, where applicable) after production, assemblyand magnetisation.

FIGS. 4 c to 4 e show alternative domain alignment patterns, which willbe described in detail later.

FIG. 5 a shows the Halbach-style resulting magnetic flux field 60, indiagrammatic form, of a part of the rotor 36 of FIGS. 3 a, 3 b with amagnetic material ring 38 formed using the magnet elements 37 with thepre-aligned magnetic domain alignment pattern 42 as shown in FIG. 4 a.This is the resulting magnetic flux field 60 when no stator 31 ispresent. In this case the rotor 36 has a backing ring 40. The rotorcomprises magnet elements, e.g. 37, arranged side-by-side continuing thearrangement as shown in FIG. 4 b. Only some of the magnetic elements 37of the rotor are shown, but it will be appreciated that the rotorcontains enough elements to form a full permanent magnet ring 38. Thering 38 has been magnetised. Once magnetised, each magnet element 37forms a magnet that has a magnetic pole located on the stator side (E)of the magnet element 37. By arranging a number of such magnet elements37 in a permanent magnet ring 38 as shown in FIG. 5 a, a multiple polemagnet ring 38 is created where more than one magnetic pole (B or F) islocated on the stator side E of the ring 38. This is done by duplicatingthe domain alignment pattern 42 shown in FIG. 4 a but with reverseddomain magnetisation directions for each subsequently added pole orelement 37.

When a magnet element 37 is arranged in a ring 38 of similar magnetelements as shown in FIG. 5 a, face D of the magnet element 37 (andentire ring 38) is the external (outer) face, pointing away from therotational centre of the rotor 36. Face E of the magnet element 37 (andentire ring 38) is the internal (inner) face, pointing towards therotational centre of the rotor. It should be noted that a magnet element37 might have curved faces D, E commensurate with the curvature of thepermanent magnet ring 38. In FIG. 4 a, the faces D, E are shown flat forclarity. Poles B and F could either be north/south or south/north poles.

When a magnet element 37 forms part of a ring of such elements that hasbeen magnetised to produce a Halbach-style resulting magnetic flux field60, each element 37 contains a portion 60 a of that resulting magneticflux field 60. The portion of the resulting magnetic flux field is likethat shown diagrammatically by the magnetic flux field (comprising fluxlines or paths) in FIG. 6 a. The magnetic flux 60 b existing outside theelement 37 is also shown for completeness. The lines represent theportion of the resulting magnetic flux field 60 a in each magnet element37 after magnetisation. The pre-aligned magnetic domains 41 of eachelement are generally aligned in a direction similar, but not exactlythe same, as the portion of resulting magnetic flux field 60 a that isultimately created in each magnet element 37. The pre-aligned magneticdomains of each element do not need to be aligned in the same manner asthe desired Halbach-style resulting magnetic flux field 60 a. In fact,deviation in the magnetic domain alignment pattern (from the idealHalbach-style resulting magnetic flux field) is possible, while stillallowing or assisting the creation of the desired Halbach-styleresulting magnetic flux field. This result is counter-intuitive. FIG. 6b shows a superposition of the portion of the resulting magnetic fluxfield 60 a and the magnetic domain alignment pattern 42 existing in eachelement 37—this illustrates the differences between the two. Whenapplying the magnetisation pattern to magnetise the permanent magnetring 38 of the rotor 36, the magnetic domain alignment pattern 42 shownin FIG. 4 a which exists in each magnet element 37 produces a desiredHalbach-style resulting magnetic flux field that is stronger at thepoles B, F on the inner face E than what would be achieved with anisotropic element or magnet elements in which the domains are alignedradially.

Referring now to FIGS. 4 a to 6 c in general, the nature of the magneticdomain alignment pattern 42 and resulting magnetic flux field 60 will bedescribed in more detail. Note that these Figures show flux fields anddomain alignment in diagrammatic form for illustrative purposes.

Each magnet element comprises magnetic domains 41 as noted earlier. Thepreferred orientation direction of each magnetic domain 41 is a functionof its angular position around the circumference of the rotor 36 anddoes not vary with radial position, as shown in FIG. 4 a. It should benoted that FIG. 4 a shows the ideal preferred magnetic domain alignmentpattern. In practice, not all magnetic domains will necessarily bealigned as shown, as some might vary from the ideal due to randomfluctuations. Also, other patterns, as will be described later, are alsopossible. The differing orientations of the magnetic domains in anelement 37 produces a magnetic domain alignment pattern 42 thatpreferably varies continuously with tangential position in direction C.Tangential position refers to the position across the width of theelement 37, or more particularly across the element 37 between thelateral edges 37 a, 37 b. The lateral edges 37 a, 37 b are those edgesthat are adjacent or proximate other elements 37 arranged in thepermanent magnet ring. The orientation of the magnetic domain alignmentpattern 42 at any position corresponds to the orientation of themagnetic domain(s) 41 at that position. The magnetic domain alignmentpattern 42 is substantially radially aligned in the centre of the poleB, F and substantially tangentially aligned on each edge of each magnetelement 37. Radially aligned refers to the direction pointing towards oraway from the centre of the permanent magnet ring 38 when the element 37is arranged in such a ring, generally in the direction of arrow G.Tangentially aligned refers to the direction perpendicular to thelateral edge, generally in the direction of arrow C.

It will be appreciated that the magnet elements have a three-dimensionalthickness, not depicted in the two-dimensional representations. It willbe appreciated that the domain alignment pattern described and shown intwo dimensions will exist throughout the thickness of the magnetelement. If a cross section were hypothetically taken through any partof the thickness of the magnet element, substantially the same domainalignment patterns depicted would exist. Following on from this, theterm “lateral edge” more generally refers to the lateral edge of themagnet element at any point throughout the thickness, such that thelateral edge in fact exists as a lateral edge surface. For simplicity,this is referred to as the lateral edge.

To produce such a magnetic domain alignment pattern 42, the radial andtangential components of the orientation of the magnetic domains 41within each magnet element 37 are aligned according to sinusoidalfunctions of the tangential position along the magnet element 37,according to the following relations:

V _(R)=cos(θ)  (1)

V _(T)=sin(θ)  (2)

where V_(R) and V_(T) are the radial and tangential components of thealignment direction vector of a magnetic domain respectively and θ isthe angular position across the magnet, varying from −90 degrees atlateral edge 37 a to +90 degrees at lateral edge 37 b.

The resulting magnetic domain alignment vector preferably rotatessmoothly with the angular position across each magnet element 37, beingsubstantially radially aligned in the centre of a magnet element (θ=0,at the pole) and being substantially tangentially aligned at the magnetelement 37 edges 37 a and 37 b, but being of opposite polarity.

In this arrangement, the magnetic domains 41 of each magnet element 37are aligned, prior to magnetisation, approximately in the direction ofthe portion of the resulting magnetic flux field 60 a that exists inthat magnet element 37 after magnetisation. However, they are notexactly aligned, as is evident from FIG. 6 b, which shows asuperposition of the domain alignment 42 and resulting magnetic fluxfield in the magnet element. The preferred magnetic domain alignmentpattern 42 and the preferred Halbach-style resulting magnetic flux field60 are different in geometry.

It will be appreciated that while the above describes the preferredmagnetic domain alignment pattern 42, exact conformance to the preferredalignment pattern is not essential for producing a Halbach-styleresulting magnetic flux field 60. Any magnetic domain alignment pattern42 could be used in which the magnetic domains 41 are aligned, prior tomagnetisation, approximately in the direction of the preferred magneticdomain alignment pattern that assists in producing a strongerHalbach-style resulting magnetic flux field.

In the general case, the magnetic domain alignment pattern 42 can be anypattern that improves or assists the production of a Halbach-style fluxfield during magnetisation. The inventors have found that aligning thedomain alignment pattern in the manner described above improves thestrength per unit of magnet material of the Halbach-style resultingmagnetic flux field 60 ultimately linked through the stator.Counter-intuitively, this domain alignment pattern 42 is not the same asthe actual resulting magnetic flux 60 a in the magnet element 37, aftermagnetisation, as can be seen in FIG. 6 b. This improvement in fluxfield strength per unit of magnetic material provides an ultimateincrease in torque provided by the motor in which the rotor is used.

However, some gains can be achieved even without using the idealpreferred domain alignment pattern shown in FIG. 4 a. Non-ideal (e.g.with random fluctuations from the ideal) alignment patterns provide somegain, as well as the alternative embodiments described below, oracceptable deviations from those alternative embodiments, which will beappreciated by those skilled in the art.

For example, more generally, the orientation of the magnetic domainalignment pattern 42 might not be substantially radial at the poles B, Fand might not be substantially tangential at the edges of the element37. The orientation might, instead, have a predominant radial componentand at least some tangential component at the poles and edgesrespectively. By predominant radial component, it is meant that themagnitude of the radial component dominates the orientation vector suchthat the vector points more in a radial direction than a tangentialdirection. This means that the orientation points predominantly,although not necessarily entirely, in the radial direction. Predominantradial component also covers the preferred case where there is only aradial component of the orientation vector, such that the orientationvector points solely or substantially in a radial direction.

By at least some tangential component, it is meant that the orientationvector has at least some tangential component so that the orientationvector points at least partially in a tangential direction. This canalso cover where the orientation vector points completely tangentially.

The more tangential the angle of the orientation vector at the edge, thelarger the increase in flux linkage through the stator, and the greaterthe benefits. The orientation angle is measured between the radiallyaligned edge 37 a, 37 b of the magnet element 37 and the orientationvector (see, for example θ in FIG. 4 c). For example, FIG. 6 c shows therelationship between a) the angle of the orientation of the domainalignment pattern 42 at the edge 37 a, 37 b of a magnet element 37 andb) the percentage of magnetic flux linking with the stator pole(relative to a magnet element with radially aligned domains) when themagnet element 37 is used in a rotor. As can be seen, where theorientation angle at the magnet element 37 edge is 0 degrees (i.e. theorientation at the edge is radially aligned), the percentage of fluxlinking is the same (100%) as for a magnet element with radial domainalignment. Where the orientation at the magnet element 37 edge is 90degrees (completely tangential), the percentage flux linking comparedwith the radially aligned element is 130%. Noticeably, there is gain ateven relatively small angles. For example, an orientation angle of 15degrees at the edge 37 a, 37 b still gives a flux linking of around105%, and there is a significant advantage at 30 degrees. Therefore, anysuitable angle of domain alignment orientation 42 at the edge 37 a, 37 bcould be used, as shown generally in FIG. 4 c.

More specifically, referring to FIG. 4 d, a domain alignment orientationat the edge (also called a “magnetic domain edge angle”) 37 a, 37 b ofaround 15 degrees could be used. This is provided a vector with at leastsome tangential component. In a more preferable case, the orientationvector at the edge has a significant tangential component. By this itmeans that the orientation vector has an angle of at least 30 degreeswith respect to the respective edge 37 a, 37 b. In a yet more preferablecase, the orientation vector at the edge 37 a, 37 b has a predominanttangential component. By this it means that the tangential componentdominates the orientation vector such that the vector points more in atangential direction than in a radial direction. By this it means thatthe orientation of the magnetic domain alignment pattern at the edgescould have components that are sufficient in magnitude to produce anorientation that differs by up to 45 degrees (or greater—towards 90degrees) from the radial direction, which can be seen in FIG. 4 e.

A preferred magnetic domain edge angle is 30 degrees, as shown in FIG. 4f. As edge angles increase, it has been found that the yield of themagnet elements during production decreases. It has been found that a 30degree magnetic domain edge angle provides an acceptable yield, whilestill providing the required flux linking. Clearly, other edge anglesmight be found to be more suitable in different applications, wherethere are different acceptable levels of yield and flux linkage.

This means that the orientation points predominantly, although notnecessarily entirely in the respective tangential or radial directions.The terms “predominant” and “significant” tangential component alsocovers the case where there is only a tangential component of theorientation vector, such that the orientation vector points solely in atangential direction.

Therefore, in general, the domain alignment pattern of a magnet element37 can be any where the orientation varies substantially continuouslyacross at least part of the magnet element 37 (e.g. from a pole to anedge) from an orientation that has a predominant radial component at apole of the magnet element to an orientation that has a least sometangential component at least one lateral edge 37 a, 37 b of the magnetelement. Clearly, the same orientation variance might take place fromthe pole to the other lateral edge 37 a, 37 b also. FIG. 4 c shows amagnet element in the general case with one possible alternative domainalignment pattern in which the edge orientations are not tangential, butrather some arbitrary angle θ with respect to the lateral edges of theelement. In this case, θ is greater than 45 degrees, but it could be 45degrees or less or even as low as 15 degrees, as described above.

Further, the variance across the element 37 might only bequasi-sinusoidal. Also, the variance of orientation might only bepredominantly continuous, due to random fluctuations in magnetic domainorientations.

It should also be noted that FIGS. 4 a and 4 c to 4 e show the magneticdomains aligned in a manner pointing “away” from the front face E. Themagnetic domains could be aligned with the domains pointing “towards”the front face E, like the right hand element in FIG. 4 b. As can beseen, the “flipped” magnetic domain direction is due to the existence ofa north or south pole at face E, as shown in FIG. 4 b. Predominantly,the magnetic domains are shown in respect of one pole for clarityreasons.

The magnetic domains of each magnet element are pre-aligned as describedabove and as shown in FIGS. 4 a-4 e by applying an external magneticfield during production of the magnet element 37. The pre-aligning ofthe magnetic domains creates an anisotropic element. Pre-aligning themagnetic domains enables more efficient creation of a permanent magneticfield in the element. Creation of the magnet element 37 is describedfurther later with respect to FIGS. 7 a to 8 c.

The resulting magnetic flux field 60 will now be described in furtherdetail. The rotor 36 has a preferred resulting magnetic flux field asshown in solid lines in FIG. 6 a, which is the Halbach-style resultingmagnetic flux field as mentioned previously. Each magnet element 37 inthe rotor 36 has a magnetic pole with a polarity as shown by arrow “B”or “F”, in FIG. 5 a. The pole is radially aligned. That is, the polecreates a resulting magnetic flux field in its vicinity that is alignedsubstantially radially towards or away (direction of arrow G) from thecentre of the rotor 36 when the magnet element 37 is arranged in apermanent magnet ring 38 with other magnet elements 37. When arranged ina ring 38, each magnet element 37 will have a pole in the same place butwith an opposite polarity to adjacent magnet elements 37, as shown bythe arrows “B” and “F” in FIG. 5 a. Therefore, the permanent magnet ringformed from the magnet elements 37 will have poles with alternatingpolarity spaced around the ring.

The portion of the resulting magnetic flux field 60 a in a magnetelement 37 traverses from its pole (B or F) to the respective adjacentopposite poles (F or B) in each adjacent element. That is, in thepreferred embodiment, the portion of the resulting magnetic flux field60 a in a magnet element 37 is aligned substantially tangential to facesD and E at the edges of the magnet element 37, as shown in FIG. 6 a. Atthe poles B, F (FIG. 5 a), the resulting magnetic flux field 60 issubstantially aligned radially towards or away from the centre of therotor 36. Therefore, in each element, the alignment of the resultingmagnetic flux field 60 a changes from substantially radially aligned tosubstantially tangentially aligned along the tangential direction, fromthe pole to the edges, 37 a and 37 b, shown by arrow “C” in FIG. 6 a.

The resulting magnetic flux field 60 produced in and around themagnetised permanent magnet ring 38 is substantially or at leastpartially constrained within the boundary defined by outer faces D ofthe magnet elements 37 forming the ring. However, the resulting magneticflux field is not necessarily totally constrained, as some might enterthe backing ring 40 (e.g. see FIG. 5 b). Therefore, the resultingmagnetic flux field 60 is significantly reduced on the external side(outer face D) of the ring 38 (and the backing ring 40, if one exists).The predominant part of the resulting magnetic flux field 60 traversingthe poles B, F of opposite polarity in the permanent magnet ring 38exist within the permanent magnet ring 38 and extend beyond the boundarydefined by inner faces E towards the stator poles 32 in a radialdirection. That is, the resulting magnetic flux field 60 extends beyondinner faces E and can couple with the magnetic flux field of the statorpoles 32 (see FIG. 5 b). The predicted actual resulting magnetic fluxfield 60 in the elements when a stator 31 is introduced to the rotor 36,is shown in FIG. 5 b. The magnetic domain alignment pattern allows formore magnetic material to be utilised in creating the resulting magneticflux field. The magnetic flux field 60 is focussed towards and into thestator 31 poles 32. This increases the magnetic flux field beyond theinner faces E of magnet elements 37 of the ring 38 to increase thetorque on the rotor 36 and, if this field is sinusoidal, can alsominimise cogging. This resulting magnetic flux field 60 is effectivelycreated by focussing the flux in the magnet elements 37 themselves, andoutside the magnet elements radially towards the stator poles 32. Thisfocussing reduces the amount of magnetic flux passing out the externalside D of the magnet ring 38. As can be seen, only a small portion ofthe magnetic flux field 60 passes out the back face D and into thebacking ring 40. The pre-alignment of the magnetic domains 41 asdescribed above produces the desired resulting magnetic flux field 60when magnetisation of the rotor ring 38 or elements 37 of the rotor ring38 takes place.

The above description of the resulting magnetic flux field 60 relates tothe preferred Halbach-style resulting magnetic flux field that is to beachieved using the magnetic domain alignment pattern 42 described above.This preferred flux field mimics as much as possible a flux fieldproduced by a large or infinite number of magnet elements formed into aHalbach array of magnets. The magnet elements 37 are oriented in therotor according to their pole orientation order to obtain this flux“focussing” towards the centre of the rotor. This is in contrast toplacing the magnet elements so that flux is “defocused” away from thecentre of the rotor. In practice, this preferred flux field might not befully achieved by the magnetic domain alignment pattern 42. In the moregeneral case, the resulting magnetic flux field 60 can be described asfollows.

Referring to FIG. 6 a, each portion of the resulting magnetic flux field60 a that exists in each magnet element 37 has an orientation thatvaries continuously over the magnet element. The orientation of theresulting magnetic flux field 60 at any point can be described as avector with a tangential component (as shown by arrow C in FIG. 6 a) anda radial component (as shown by arrow G in FIG. 6 a). Across the widthof a magnet element 37, that orientation varies from an orientation thathas a predominant radial component at the pole (B or F) to anorientation that has a predominant tangential component at the edges ofthe magnet element 37 adjacent other magnet elements 37 in the permanentmagnet ring 38. Further, across the depth (from face E to face D) of themagnet element 37, the orientation varies from an orientation that has apredominant radial component at an edge corresponding to the inner faceE of the permanent magnet ring 38 to an orientation that has apredominant tangential component at an edge corresponding to the outerface D of the permanent magnet ring 38. The orientation typically variesnon-linearly over the magnet element 37.

By predominant radial component, it is meant that the magnitude of theradial component dominates the orientation vector such that the vectorpoints more in a radial direction than a tangential direction.Predominant radial component also covers the case where there is only aradial component of the orientation vector, such that the orientationvector points solely in a radial direction. By predominant tangentialcomponent, it is meant that the magnitude of the tangential componentdominates the orientation vector such that the vector points more in atangential direction than in a radial direction. Predominant tangentialcomponent also covers the case where there is only a tangentialcomponent of the orientation vector, such that the orientation vectorpoints solely in a tangential direction.

Preferably, when no stator 31 is present, the radial and tangentialcomponents of the resulting magnetic flux field 60 at the inner surfaceE varies substantially sinusoidally proceeding along the magnet indirection C, according to the following relations:

V _(R)=cos(θ)  (3)

V _(T)=−sin(θ)  (4)

where V_(R) and V_(T) are the radial and tangential components of theflux field direction vector respectively and θ is the angular positionacross the magnet element 37, varying from −90 degrees at one edge 37 ato +90 degrees at the opposite edge 37 b.

FIGS. 6 d and 6 e show the comparison of the tangential and radialcomponents of the resulting flux field along the inner surface of themagnet element 37. As can be seen, they follow sine and cosine forms.The graphs in FIGS. 6 d, 6 e also shows a comparison to the tangentialand radial components of the resulting magnetic flux field along theinner surface when using standard elements with radially alignedmagnetic domains.

In addition, the portion of the resulting magnetic flux field 60 boutside each magnet element 37 and between adjacent poles B, F extendingbeyond the boundary defined by the inner face E of the permanent magnetring 38 has an orientation that varies continuously. Again, theorientation of the resulting magnetic flux field 60 at any point outsidethe inner face E of each magnet element 37 can be described as a vectorwith a tangential component (as shown by arrow C in FIG. 6 a) and aradial component (as shown by arrow G in FIG. 6 a). Between the poles B,F, the orientation varies from an orientation that has a predominantradial component at the pole to an orientation that has a predominanttangential component at the mid-point between the poles. Further,extending radially inwards from the inner face E to the centre ofrotation of the rotor 36, the orientation varies from an orientationthat has a predominant radial component at the inner face E to anorientation that has an increasingly tangential component with distancefrom the inner face E. The orientation typically varies non-linearlybetween the poles B, F and extending beyond the inner face E.

During use, when current is applied to the stator, a net torque isgenerated between the rotor 36 and stator 31, causing the rotor 36 torotate with respect to the stator 31. In addition to this net torque,the motor will also experience a rotor position dependent torque thatcauses the rotor 36 to rotate in the direction in which the reluctanceof the magnet flux path is reduced. Likewise the rotor 36 will opposemovement in the direction that increases reluctance. This torque iscommonly referred to as cogging, or reluctance, torque. Cogging torqueoccurs because there are variations in the reluctance as the angularposition of the rotor 36 changes, and the effect of this variation intorque can lead to unwanted vibrations. The resulting magnetic fluxfield 60 of the present invention alleviates this to at least someextent. In the present invention, a sinusoidal flux distribution isproduced by the magnet rotor ring 38 on the stator side E of the rotor36. A sinusoidal flux distribution makes it easier to cancel coggingforces through manipulation of the stator pole 32 tip geometry sincethere are no higher order torque harmonics, cancellation of thefundamental frequency being required.

Each element could be produced by a press 78 as shown in FIG. 7 a. Thepress comprises a die 70 formed of a first portion 70 a made ofnon-magnetic steel and a second portion 70 b, made of magnetic steel.The die can preferably have a tungsten carbide layer 70 c to providewear resistance. Magnetic steel inserts 79 a, 79 b are placed in thefirst portion 70 a to avoid saturation in the steel of the punch duringdomain alignment. The die 70 defines a magnet cavity 72. The press 78also comprises a two part lower hydraulic punch 71, and a two part upperhydraulic punch 73. The upper and lower punches 71, 73 are formed ofmagnetic steel. Punch 71 has a non-magnetic cap 71 a. The upper punchhas a non-magnetic insert 79 c. Preferably, both the non-magnetic cap 71a and non-magnetic insert 79 c are made of tungsten carbide for wearresistance. An electromagnetic coil 74 resides around the upper punch. Atop plate 75, base plate 76 and two posts 77 a, 77 b provide the pressstructure. These are made of magnetic steel.

A possible process for promoting the domain alignment pattern 42 withina magnet using a wet slurry of ferrite material is as follows. The press78 is set to the open position. In such a state the upper punch 73 ismoved up some distance away from die 70 providing access to the magnetcavity 72. The lower punch 71 retracts downwards a short distance. A wetslurry of magnetic material (not shown) such as that typically used inindustry for the moulding of high strength ferrite magnets is placed inthe magnet cavity 72. The individual magnetic domains to be aligned aredefined by the very finely ground magnetic material. A permeable gauzematerial 79 is placed in the gap between the faces of the stationary die70 and the upper punch 73. The upper punch 73 moves down to close thegap between the stationary die 70 and upper punch 73 face. A DC currentis applied to the electromagnetic coil 74, which acts to generate amagnetic flux field in the magnetic circuit provided by the press 78components. This is described further below in respect of FIGS. 7 b, 7c. The combination of the geometry and the location of the magnetic andnon-magnetic material is such that the intended magnetic domainalignment pattern is promoted within the magnet cavity.

The lower punch 71 is then extended steadily upwards, compressing thematerial. The applied pressure forces liquids within the material outthrough the permeable gauze material located between the die 70 andupper punch 73 faces. The quantity of liquid within the magnet cavity issignificantly reduced during this step. When the magnetic material hasbeen sufficiently compressed, the lower punch 71 is no longer extendedbut is held in position. At this stage the magnet has reached the greenstate. In this state the magnetic domains are aligned and are no longerfree to rotate relative to each other. To ensure that both the press 78and magnet element 37 are demagnetised to enable further processing, theconstant DC current is changed to be time varying such that it issinusoidal in nature and whose magnitude diminishes towards zero. Whenthe peaks of the current have been reduced to zero the magnet and press78 can be considered to be demagnetised. The element is demagnetised toavoid the possibility of the element disintegrating. The upper punch 73is then retracted upwards and the gauze material 79 removed to leave theupper surface of the magnet exposed. The lower punch 71 is then furtherextended a short distance so that the green magnet is separated from thedie 70 and can be removed. The green magnets are then left to dry for aperiod of time. The green magnets are then sintered within a kiln athigh temperatures. The remaining liquid is extracted from the magnetduring this stage. After cooling the magnet is ready for use or ifnecessary additional operations such as grinding are possible.

FIG. 7 b shows the applied magnetic flux field to the press 78, and inparticular the cavity 72 in order to align the magnetic domains of themagnet element 37 in the desired manner. FIG. 7 c shows the magneticflux field in the cavity 72 in more detail. The top plate 75, base plate76 and posts 77 a, 77 b along with the insert 79 a, 79 b, lower punch71, magnetic portion of die 70 b and upper punch 73 combine to form aloop that directs magnetic field flux through the tool and into thecavity in such a way as to produce a resulting magnetic flux field inthe cavity 72 (and magnet element 37). This flux field is generally inthe same direction as the desired domain alignment pattern 42. This fluxfield promotes the desired alignment of the magnetic domains 41 withinthe magnet element. For ferrite material, a flux density throughout themagnet cavity 72 equal to the remanence flux density B_(r) of the magnetelement is typically sufficient to ensure that the magnet domains of thematerial are well aligned. However, a flux density less than B_(r) couldstill be applied although in such a case the magnetic domains 41 may notbe fully aligned with the magnetic field that exists within the cavityand therefore being less desirable but still acceptable. Though only onemagnet cavity 72 is shown, for economic manufacture multiple magnetcavities 72 could be readily created within a single die 70 with theprocess for producing the alignment pattern within a magnet replicatedfor each cavity.

Alternatively each magnet element 37 could be produced in an injectionmoulding tool 80 as shown in FIG. 8 a. The injection moulding tool 80comprises two main sections 81, 82. The first section 81 is the fixedportion of the tool and the second section 82 is the moving portion ofthe tool. The first section comprises a fixed magnetic steel plate 83 a,83 b, a fixed non-magnetic steel insert 84 and a fixed plastic injectionrunner 85. The second section 82 comprises a moving magnetic steelinsert 86, a moving magnetic steel plate 89, moving permanent magnetmaterial 87 a, 87 b, moving flux directing plates 90 a, 90 b and amoving non-magnetic steel 88. The first and second sections 81, 82 arearranged to form a mould cavity 91 for producing a magnet element 37.The moving permanent magnet material 87 a, 87 b can be Samarium cobaltpermanent magnet material.

The magnetic steel plate 83 a, 83 b is attached to an injection mouldingmachine, with the injection moulding machine being capable of injectionmoulding blends of plastic and particles of magnetic material into thecavity 91.

FIG. 8 b show the magnetic domain alignment flux field applied to themagnetic element 37. FIG. 8 c shows the cavity 91 and magnetic domainalignment flux field in more detail. This flux field is generally in thesame direction as the desired domain alignment pattern 42. Afterproducing the magnetic element 37 using the injection moulding tool 80,the magnetic element 37 is fully magnetised ready for assembly into themagnet ring 38 without the need for demagnetising for furtherprocessing. The magnet element 37 may be optionally demagnetised toenable easy assembly into the magnet ring 38 and then the assembledmagnet ring 38 re-magnestised.

The magnetic steel 83 a, 83 b, permanent magnet material 87 a, 87 b,flux directing plates 90 a, 90 b and moving magnetic steel 86, 89combine to form a loop that directs magnetic field flux through the tool80 in such a way as to produce a magnetic flux field in the cavity 91and magnetic element 37. This flux field promotes the desired alignmentof the magnetic domains 41 within the plastic material with particles ofmagnetic material in the cavity 91. As can be seen in FIG. 8 c, themagnetic flux field that is set up within the cavity 91 and magnetelement 37 is such that it pre-aligns the magnetic domains 41 in thedesired magnetic domain alignment pattern 42. Though only one magnetcavity 91 is shown, for economic manufacture multiple magnet cavities 91could be readily created within a single die 80 with the process forproducing the alignment pattern within a magnet replicated for eachcavity.

The press shown in FIG. 7 a could be used to produce ferrite magneticelements from dry ferrite powder or wet ferrite slurry, or alternativelymagnet elements from neodymium wet or dry powder or slurry. Acombination of these two magnetic materials, or others could also beused in the press of FIG. 7 a.

The injection moulding tool 80 of FIG. 8 a could produce magneticelements of polymer bonded ferrite, or neodymium-iron-boron, or a blendof ferrite and neodymium-iron-boron or any other polymer bonded magneticmaterial.

It should be noted that slurry of ferrite and/or neodymium-iron-boronmaterial or alternatively polymer bonded ferrite and/orneodymium-iron-boron is made up of micron sized magnetic particles. Theparticles are this small so that they essentially contain only a singlemagnetic domain, which is effectively the building block of a completedmagnet that looks like the diagrammatic magnet element 37 of FIGS. 4 ato 4 e. In an isotropic magnet element, these domains are randomlyaligned. In the slurry of ferrite and/or neodymium material, the domainsare free to rotate in the water, unless aligned by a magnetic field,until the water is pressed out and the particles, or domains, are“squashed” together to form a solid—then this results in an anisotropicmagnetised magnet. When magnetized, the anisotropic magnet element willhave a higher magnetic flux density than an equivalent isotropic magnetelement.

In the injection moulding process, the domains are mixed with a polymerbinder that is melted in the barrel of an injection moulder prior toinjection into the cavity. The particles are relatively free to rotatein the molten polymer binder, unless aligned by a magnetic field. If themagnetic domains are aligned by a magnetic field until the binderfreezes in the cavity, they are locked in place and then this againresults in an anisotropic magnetised magnet.

In the case of the pressed magnet the magnet is green and ismechanically very weak. To enable the magnet to be handled afterpressing and through the sintering process without disintegrating, thegreen magnet is demagnetised before removal from the cavity 72.

To prevent demagnetisation of the magnet element 37 once produced, agrade of magnetic material should be used that shows gooddemagnetisation characteristics. That is, preferably a grade thatexhibits a B-H curve with a knee in the third quadrant, such as shown inFIG. 14.

Once the magnet elements have been produced, they can be assembled inany suitable manner to form the magnetic ring for the rotor 36 asdescribed above. The ring can be magnetised using any suitable method,to produce the desired Halbach-style resulting magnetic flux field 60.For example, the rotor 36 could be placed on and mechanically alignedwith a magnetising head. The head would be a strengthened fixturecapable of high current and field. A bank of capacitors would then bedischarged through the windings of the head, producing the magnetisingalignment field necessary to produce the resulting magnetic flux field.

FIG. 16 shows one possible magnetiser 169. This produces flux linesdesigned to match up with FIG. 5 a. FIG. 16 shows an all steel back iron(laminated silicon steel) 170 with high saturation flux density 160, aset of slots between the poles 161, coil windings 162 in the slots, andair gap 163 between the magnetiser poles 161 and the magnet elements 37.A backing steel 40 is behind the magnet elements 37, and there is asmall air gap 164 between the elements 37. This magnetiser 169 producesthe resulting magnetic flux field in the rotor.

Magnetisation of the overall rotor is used when individual elements 37are demagnetised during the production process to avoid disintegration.If the elements 37 are not demagnetised during production, then it isnot necessary to magnetise the rotor as described above. That is, therotor could be assembled from magnetised elements 37, such that whenarranged in a ring for the rotor, the Halbach-style resulting magneticflux field is already present. The benefits of having pre-aligneddomains will still apply, in that the magnets will provide an overallstronger Halbach-style resulting magnetic flux field per unit of magnetmaterial.

An embodiment of the invention might comprise a washing machine with amotor as described above, or another embodiment might comprise the motoritself, or the rotor itself. Alternatively, the rotor could be used inanother application, such as a power generation apparatus. Anotherembodiment of the invention could comprise a magnet element, asdescribed above.

A washing machine using the motor described could take one of manyforms. For example, referring to FIG. 9, one embodiment comprises a toploading washing machine with an outer wrapper and a tub suspended withinthe wrapper. A rotating drum with perforated walls is disposed in androtatable within the suspended tub. A motor, comprising a stator androtor as previously desired, is coupled to the rotating drum via arotational shaft. The motor can be operated by a controller to spin andoscillate the rotating drum to carry out washing of clothes. Themagnetic elements used in the rotor reduce cogging of the motor and themagnetic field in the rotor increases the torque of the motor relativeto the rotor size, weight and volume of ferrite. These make the motor asa whole less expense and operate more efficiently.

Referring to FIG. 10, another embodiment comprises a front loadinghorizontal axis washing machine with an outer wrapper and a rotatingdrum housing suspended in the outer wrapper. A rotating drum is disposedin and rotatable within the rotating drum housing. A door providesaccess to the rotating drum for introducing or removing clothing to bewashed. A gasket provides a seal between the door and the rotating drum.A motor, comprising a stator and rotor as previously desired, is coupledto the rotating drum via a rotational shaft. The motor can be operatedby a controller to spin and oscillate the rotating drum to carry outwashing of clothes. The magnetic elements used in the rotor reducecogging of the motor and the magnetic field in the rotor increases thetorque on the rotor. These make the motor as a whole operate moreefficiently.

Referring to FIG. 11, another embodiment comprises a top loading or tiltaccess horizontal axis washing machine. The washing machine has an outerwrapper and a tub suspended within the outer wrapper. A rotating drumcan rotate within the tub. Clothes can be introduced and taken from therotating drum through an opening in the top of the drum. A motor,comprising a stator and rotor as previously desired, is coupled to therotating drum via a rotational shaft. The motor can be operated by acontroller to spin and oscillate the rotating drum to carry out washingof clothes. The magnetic elements used in the rotor reduce cogging ofthe motor and the magnetic field in the rotor increases the torque onthe rotor. These make the motor as a whole operate more efficiently.

FIG. 12 shows a tilt loading horizontal axis washing machine. Thewashing machine has an outer wrapper and a tub suspended within theouter wrapper. A rotating drum can rotate within the tub. Clothes can beintroduced and taken from the rotating drum by tilting the drum. Amotor, comprising a stator and rotor as previously desired, is coupledto the rotating drum via a rotational shaft. The motor can be operatedby a controller to spin and oscillate the rotating drum to carry outwashing of clothes. The magnetic elements used in the rotor reducecogging of the motor and the magnetic field in the rotor increases thetorque on the rotor. These make the motor as a whole operate moreefficiently.

It will be appreciated that FIGS. 9 to 12 show just four examples ofwashing machines that could utilise a motor with a rotor containingmagnetic elements produced in the manner described above. Otherembodiments of the present invention could comprise other washingmachines be envisaged by those skilled in the art, operated by a motoras described above.

FIG. 13 shows the predicted relative togging performance of a) rotorswith standard magnetic field patterns and radially oriented magneticdomains, and b) rotors with equal size and volume of magnet materialwith magnetic domains oriented to follow the Halbach type fieldpatterns.

It will be appreciated that magnet elements made from material otherthan hard ferrite are possible. For example, neodymium-iron-boron orSamarium-Cobalt or other magnet material could be used, or a combinationof magnetic materials. Further, magnetic material(s) bonded into apolymer could be used.

It will be appreciated the rotor or motor according to the embodimentsabove could be used in another applications, such as a power generationapparatus.

It will be appreciated that the magnet element 37 described ispreferred, although other configurations of magnet element with domainalignment patterns are possible, that when combined form an equivalentdomain alignment pattern like that shown in FIGS. 4 a, 4 b or FIGS. 4 cto 4 e. For example, a magnet element might in fact comprise just onehalf of the magnet element 37 shown in FIG. 4 a. This is shown in FIG.15 a. This alternative magnet element 150 has a magnetic domainalignment pattern 151 from one half of the magnet domain alignmentpattern 42 shown in FIG. 4 a. The magnetic domain alignment pattern 151has a pole 153 at one lateral edge 154 b of the element 150. Theorientation varies substantially continuously across the magnet element150 between its lateral edges 154 b, 154 a from an orientation that hasa predominant radial component at the pole 153 of the magnet element atone lateral edge 154 b to an orientation that has a least sometangential component on the other lateral edge 154 a of the magnetelement 150. It will be appreciated that the nature of the magneticdomain alignment pattern is exactly the same as one half of thealignment pattern shown in FIG. 4 a, and the description there can beextended to apply to this embodiment. The alternative embodiments ofdomain alignment patterns described in relation to the magnet element 37(see e.g. FIGS. 4 c to 4 e) can also apply to the magnet element 150.that is, in such a element as 150, its domain alignment pattern has anorientation that varies substantially continuously across the magnetelement between its lateral edges from an orientation that has apredominant radial component at a pole of the magnet element at onelateral edge to an orientation that has a least some tangentialcomponent the other lateral edge of the magnet element.

It will also be appreciated that an alternative magnet element couldalso be made that has a domain alignment pattern that is the mirrorimage of that shown in FIG. 15 a, as shown in FIG. 15 b. Elements 150and a mirror image element could be assembled resulting in an elementlike that in FIG. 4 a. Alternatively, Element 150 could be assembledwith another element 150 rotated 180 degrees around the radial axis,resulting in an element like that of FIG. 4 a.

The elements 150 of FIGS. 15 a, 15 b could be arranged together toproduce a rotor as described above. For example, as shown in FIG. 15 c,two such elements could be brought together arranged side-by-side in arotor ring, to effectively produce an element 37 like that shown in FIG.4 a. Alternatively, as shown in FIG. 15 d, the position of the elements150 could be reversed. Any such combination of elements 150 could thenbe arranged in a ring 38 to produce the required domain alignmentpattern. The magnet elements of alternative embodiments could be made inthe press 78 or injection moulder 80 described above.

Alternatively, a magnet element 37 could have poles at the edges, andtangentially aligned domains in the centre. A ring could be assembledfrom such elements.

In the preferred embodiment described above, when the magnet elements 37are arranged in a ring, they are arranged directly adjacent to eachother, such that a lateral edge of one magnet elements is touching orvery near the corresponding lateral edge of an adjacent magnet element37. In an alternative embodiment as shown in FIG. 3 f, there could bespacer elements e.g. 171 between the lateral edges of one or moreadjacently arranged magnet elements 37. Each spacer element could bemade from magnetic steel, or other magnetic material such as hardferrite, neodymium-iron-boron or a combination, or a bonded magneticmaterial, or other magnetic or non-magnetic material. Where magneticmaterial is used, the magnetic domains could be aligned in a suitabledomain alignment pattern to assist the production of a strongerHalbach-style magnetic flux field per unit magnet in the rotor overall.Such a flux field could be an anisotropic tangentially aligned domainpattern. It will be appreciated that in this specification that whenreferring to adjacently arranged or proximate magnetic elements 37, thisdoes not preclude having a spacer elements between the correspondinglateral edges of such adjacently arranged or proximate magnetic elements37.

FIG. 17 shows an alternative embodiment of a magnet element 170, whichcomprises a chamfer 171. The chamfer is placed on each intersection ofthe inner face E of the element and its lateral edge 175. Only onechamfer is shown, but a magnet element could have a chamfer on bothlateral edges 175. Multiple elements 170 can be arranged in an adjacentfashion with their respective chamfers aligned. The chamfer 171 reducescogging.

The chamfer has an angle 172, and a cross-sectional area “A” 173. Theexact shape of the chamfer (in terms of chamfer size and angle) is notcritical. The effect of the chamfer is approximately correlated to thecross-sectional area A 173 of the chamfer. For a given magnetic domainedge angle there are multiple chamfer sizes and angles that all providea low cogging solution.

Possible chamfer areas for particular edge angles are as follows:

Magnetic Domain Area removed by chamfer Edge Angle to reduce cogging 15°1.5 mm² 30° 1.0 mm² 45° 0.5 mm² 60° 0.05 mm²

The above chamfer 171 dimensions are suitable for one type of rotor. Itwill be appreciated by those skilled in the art that the area 173 ofchamfer 171 for any particular edge angle will differ depending onrotor/magnet element specifications. Those skilled in the art would beable to determine the correct area of chamfer 171 by selecting thatwhich provides the required cogging performance.

FIGS. 18 a to 18 c show various magnet elements 170 with chamfers 171arranged in an adjacent manner. The Figures show adjacent magnetelements with 30°, 60° and 90° magnetic domain edge angles respectively.For completeness, the magnetic domain alignment patterns 42 andresulting magnetic flux fields 60 are shown on each.

FIG. 19 indicates how utilising magnet elements with chamfers improvescogging performance over using magnet elements without chamfers. Thegraph in FIG. 19 shows the relative cogging torque produced in a rotorconstructed from magnet elements with chamfers as described above,versus the relative cogging torque produced in a rotor constructed frommagnet elements without chamfers. In this case, the chamfer has radialand tangential chamfer dimensions equal to 1.45 mm and each magnetelement has a 30° magnet domain edge angle. The graph indicates thatcogging torque is significantly reduced in the case where chamferedmagnets are utilised.

FIG. 20 shows a perspective view of a magnet element 200 with chamferededges 201.

The chamfers provide an additional advantage of enabling the magnetelements 200 to key into place on the core ring 210 of a rotor duringproduction, as shown in FIG. 21. Protrusions 211 in the core ring assistkeying and enable accurate positioning of the magnets. The chamfers alsoimprove the retention of magnet elements in place via overmoulding.

The type of magnetic material used to construct a magnet element can beselected according to the magnetic domain edge angle. As describedpreviously, FIG. 6 c shows the ideal relationship between flux linkageand magnetic domain edge angle. As the magnetic domain edge angleincreases towards 90°, the flux linkage increases. But, in practice, asthe magnetic domain edge angle increases towards 90°, the resultingmagnetic flux density decreases at the back edge of the rotor ring (side“D” in FIG. 5 a). If the level of flux density is too small,demagnetisation occurs, which is undesirable. Selecting a differentmagnetic material for the magnetic element can reduce the susceptibilityto demagnetisation, thus enabling a higher magnetic domain edge angle tobe used.

FIG. 22 shows the demagnetisation curve for three types of magnetmaterials, being N, B and H materials. As the magnetic domain edge angleincreases, the operating point of the magnetic material at the back edgeof the rotor ring will move to a more negative H region in the BH curve,resulting in a lower B value. Once the knee of the BH curve is reached,magnetisation drops off rapidly, resulting in demagnetisation. Byselecting another magnetic material, the “operating” region of themagnetic material before encountering the knee is increased for aparticular edge angle. Therefore, by selection of another material,demagnetisation can be avoided for higher edge angles. Typically, forlower edge angles an N magnet material will be selected, moving towardsa B and then H magnet material for higher edge angles. Materials withknees that occur at a more negative B value typically have a lowermagnetic strength. Therefore, a material will be selected to maximiseflux coupling while avoiding demagnetisation at the desired edge angle.

FIG. 23 is a graph showing generically the effect of flux linkage versusmagnetic domain edge angle using different magnet material. An N gradematerial provides an increase of flux linkage between 0 and edge angle 1(EA1). At EA 1 the demagnetisation is unacceptable, so for edge anglesbetween EA1 and EA2 a B grade material is used. The flux linkage is lessthan for the equivalent edge angle than if the N grade material wereused, but the B grade material provides a more acceptable level ofmagnetisation. Above an edge angle EA 2, a H grade material can be used.Again, it has lower flux linkage, but provides acceptable magnetisationcharacteristics. The appropriate type of material can be selected basedon the desired magnetic domain edge angle for the magnet element.However, it has been found that the gain in flux linkage for higher edgeangles has diminishing returns. Therefore, in many cases, a lower edgeangle might be selected, as it allows for a magnet grade of higherstrength to be used, while still providing an acceptable flux linkage.

FIG. 24 shows a possible arrangement of the backing steel of the rotor.Here the backing steel 240 is overlayed to create a “joggle” 241. Thejoggle reduces the airgap behind one magnet as the steel strip 240 fromthe second layer 240 b ramps up over the start of the first layer 204 a.Benefits are:

a) a better retention of magnets on the core ring, and

b) avoidance of an increased reluctance path for the flux passingthrough the magnet into the backing ring.

1. A rotor comprising: a plurality of magnet elements with two lateraledges each with magnetic domains aligned anisotropically to form adomain alignment pattern, the plurality of magnets being arranged toform a permanent magnet ring with an inner face and an outer face, saidpermanent magnet ring being between 150 mm and 400 mm in diameter, lessthan 100 mm in height and less than 20 mm thick, and a rigid supportholding said magnet elements in said ring arrangement, wherein themagnetic domain alignment pattern in each magnet element has anorientation that varies substantially continuously across at least partof the magnet element between its lateral edges from an orientation thathas a predominant radial component at a pole of the magnet element to anorientation that has a least some tangential component at one lateraledge of the magnet element, wherein the magnet elements are magnetisedto produce a resulting magnetic flux field.
 2. (canceled)
 3. A rotoraccording to claim 1 wherein each magnet element has the pole positionedbetween the magnet element's lateral edges and the magnetic domainalignment pattern in each magnet element has an orientation that variessubstantially continuously across the width of the magnet element froman orientation that has a predominant radial component at the pole ofthe magnet element to an orientation that has a least some tangentialcomponent at both lateral edges of the magnet element.
 4. (canceled) 5.A rotor according to claim 3 wherein at both lateral edges theorientation of the magnetic domain alignment pattern has a significanttangential component, and the significant tangential component resultsin the magnetic domain alignment pattern having an orientation of atleast 15 degrees, with respect to the lateral edges. 6-10. (canceled)11. A rotor according to claim 1 wherein the radial and tangentialcomponents of the orientation of the magnetic domain alignment patternwithin the magnet element varies sinusoidally according to:V _(R)=cos(θ), andV _(T)=sin(θ) Where V_(R) and V_(T) are the radial and tangentialcomponents of the orientation respectively and θ is the angular positionacross the magnet element, varying from substantially −90 degrees at onelateral edge to substantially +90 degrees at the opposite lateral edge.12-15. (canceled)
 16. A rotor according to claim 1 wherein the resultingmagnetic flux field has poles with alternating polarity spaced aroundthe ring, the poles being aligned radially with respect to the permanentmagnet ring, and wherein the resulting magnetic flux field of thepermanent magnet ring traverses between adjacent poles of oppositepolarities and between those poles is focused to extend beyond theboundary defined by the inner face, but remain at least partiallyconstrained within the boundary defined by the outer face of thepermanent magnet ring.
 17. (canceled)
 18. A rotor according to claim 16wherein the portion of the resulting magnetic flux field in each magnetelement has an orientation that varies substantially continuously overthe magnet element wherein: across the width of the magnet element, theorientation varies from an orientation that has a predominant radialcomponent at the pole to an orientation that has a predominanttangential component at the edges of the magnet element adjacent othermagnet elements in the permanent magnet ring, and across the depth ofthe magnet element, the orientation varies from an orientation that hasa predominant radial component at an edge corresponding to the innerface of the permanent magnet ring to an orientation that has apredominant tangential component at an edge corresponding to the outerface of the permanent magnet ring. 19-23. (canceled)
 24. A rotoraccording to claim 1 wherein for each magnet element, the magneticdomains were aligned during production using a press or injectionmoulding tool comprising one or more elements defining a cavity, and anapparatus for applying a magnetic flux field, wherein the apparatusproduces a magnetic field in the cavity similar in nature to the desiredmagnetic domain alignment pattern in the element.
 25. A rotor accordingto claim 1 wherein the rotor is utilised in the drive motor of a washingmachine comprising an electronically commutated motor, a stator of themotor having windings energisable to cause rotation of the rotor, saidstator being coupled to a non-rotating tub or housing of the washingmachine, said rotor being coupled to a rotating drum of the washingmachine. 26-29. (canceled)
 30. A motor for use in a washing machine,said motor comprising: a stator having at least three phase windings,each phase winding being formed on a plurality of radially extendingstator teeth, a rotor as defined in any preceding claim, concentric withsaid stator with the permanent magnet ring outside said stator teeth andsaid rotor poles facing the ends of said stator teeth.
 31. A method ofproducing a rotor comprising the steps of: producing a plurality ofmagnet elements comprising permanent magnet material with two lateraledges each with magnetic domains aligned anisotropically to form adomain alignment pattern, wherein the magnetic domain alignment patternin each magnet element has an orientation that varies substantiallycontinuously across at least part of the magnet element between itslateral edges from an orientation that has a predominant radialcomponent at a pole of the magnet element to an orientation that has aleast some tangential component at one lateral edge of the magnetelement, arranging and retaining the magnet elements into a permanentmagnet ring in a rigid support, and magnetising the magnet elements toproduce a resulting magnetic flux field.
 32. (canceled)
 33. A methodaccording claim 31 wherein the step of producing the plurality of magnetelements comprises applying an external magnetic flux field to eachmagnet element to align the magnetic domains.
 34. A method according toclaim 31 wherein each magnet element has the pole positioned between themagnet element's lateral edges and applying the external magnetic fluxfield to a magnet element aligns its magnetic domains such that themagnetic domain alignment pattern in the magnet element has anorientation that varies substantially continuously across the width ofthe magnet element from an orientation that has a predominant radialcomponent at the pole of the magnet element to an orientation that has aleast some tangential component at both lateral edges of the magnetelement.
 35. (canceled)
 36. A method according to claim 34 wherein atboth lateral edges the orientation of the magnetic domain alignmentpattern has a significant tangential component, and the significanttangential component results in the magnetic domain alignment patternhaving an orientation of at least 15 degrees, with respect to thelateral edges. 37-40. (canceled)
 41. A method according to claim 31wherein the radial and tangential components of the orientation of themagnetic domain alignment pattern within the magnet element variessinusoidally according to:V _(R)=cos(θ), andV _(T)=sin(θ) Where V_(R) and V_(T) are the radial and tangentialcomponents of the orientation respectively and θ is the angular positionacross the magnet element, varying from substantially −90 degrees at onelateral edge to substantially +90 degrees at the opposite lateral edge.42-50. (canceled)
 51. A rotor comprising: a plurality of magnet elementswith two lateral edges each with magnetic domains alignedanisotropically to form a domain alignment pattern, the plurality ofmagnets being arranged to form a permanent magnet arrangement, and arigid support holding said magnet elements in said arrangement, whereinthe magnetic domain alignment pattern in each magnet element has anorientation that varies substantially continuously across at least partof the magnet element between its lateral edges from an orientation thathas a predominant radial component at a pole of the magnet element to anorientation that has a least some tangential component at one lateraledge of the magnet element, wherein the magnet elements are magnetisedto produce a resulting magnetic flux field.
 52. A magnet element forassembly into a ring of magnet elements to form part of a rotor, themagnet element having two lateral edges each with magnetic domainsaligned anisotropically to form a domain alignment pattern, wherein themagnetic domain alignment pattern in the magnet element has anorientation that varies substantially continuously across at least partof the magnet element between its lateral edges from an orientation thathas a predominant radial component at a pole of the magnet element to anorientation that has a least some tangential component at one lateraledge of the magnet element.
 53. (canceled)
 54. A magnet elementaccording to claim 52 wherein the pole is positioned between the magnetelement's lateral edges and the magnetic domain alignment pattern ineach magnet element has an orientation that varies substantiallycontinuously across the width of the magnet element from an orientationthat has a predominant radial component at the pole of the magnetelement to an orientation that has a least some tangential component atboth lateral edges of the magnet element.
 55. (canceled)
 56. A magnetelement according to claim 54 wherein at both lateral edges theorientation of the magnetic domain alignment pattern has a significanttangential component, wherein the significant tangential componentresults in the magnetic domain alignment pattern having an orientationof at least 15 degrees, with respect to the lateral edges. 57-61.(canceled)
 62. A magnet element according to claim 52 wherein the radialand tangential components of the orientation of the magnetic domainalignment pattern within the magnet element varies sinusoidallyaccording to:V _(R)=cos(θ), andV _(T)=sin(θ) Where V_(R) and V_(T) are the radial and tangentialcomponents of the orientation respectively and θ is the angular positionacross the magnet element, varying from substantially −90 degrees at onelateral edge to substantially +90 degrees at the opposite lateral edge.63-81. (canceled)
 82. A rotor according to claim 51 wherein for eachmagnet element, the magnetic domains were aligned during productionusing a press or injection moulding tool comprising one or more elementsdefining a cavity, and an apparatus for applying a magnetic flux field,wherein the apparatus produces a magnetic field in the cavity similar innature to the desired magnetic domain alignment pattern in the element.83. An appliance with a drive motor, the drive motor comprising astator, and a rotor according to claim
 1. 84. A rotor according to claim3 wherein at both lateral edges the orientation of the magnetic domainalignment pattern has a significant tangential component, and thesignificant tangential component results in the magnetic domainalignment pattern having an orientation of at between 20 to 35 degrees,with respect to the lateral edges.
 85. A rotor according to claim 3wherein at both lateral edges the orientation of the magnetic domainalignment pattern has a significant tangential component, and thesignificant tangential component results in the magnetic domainalignment pattern having an orientation of substantially 30 degrees,with respect to the lateral edges.
 86. A method according to claim 34wherein at both lateral edges the orientation of the magnetic domainalignment pattern has a significant tangential component, and thesignificant tangential component results in the magnetic domainalignment pattern having an orientation of between 20 degrees and 35degrees, with respect to the lateral edges.
 87. A method according toclaim 34 wherein at both lateral edges the orientation of the magneticdomain alignment pattern has a significant tangential component, and thesignificant tangential component results in the magnetic domainalignment pattern having an orientation of substantially 30 degrees,with respect to the lateral edges.
 88. A magnet element according toclaim 54 wherein at both lateral edges the orientation of the magneticdomain alignment pattern has a significant tangential component, whereinthe significant tangential component results in the magnetic domainalignment pattern having an orientation of between 20 degrees to 35degrees, with respect to the lateral edges.
 89. A magnet elementaccording to claim 54 wherein at both lateral edges the orientation ofthe magnetic domain alignment pattern has a significant tangentialcomponent, wherein the significant tangential component results in themagnetic domain alignment pattern having an orientation of substantially30 degrees, with respect to the lateral edges.